Very young children's comprehension of others' emotional states and their interactions with persons in distress were investigated. Twenty-four mother-child pairs were studied for a 9-month period. The children were 9, 15, or 21 months old at the beginning of the study. Trained mother observers recorded their children's responses to naturally occurring emotions and to simulated distresses. Between 1 and 2 years of age there were several significant developmental changes in children's reactions to witnessed distress in another person; with increasing age, children cried less, sympathized more, showed less amusement, more imitation, and slightly more aggression. A similar developmental progression appeared when the child was the cause of another's distress or injury. When children caused distress to someone, their reactions were sometimes intense and ambivalent and included self-punitive and reparative or remorseful responses as well. The findings begin to provide developmental norms for how children are affected by emotions in their environments.